CLEANUP: Prevent channel-t.h from being detected as C++ by GitHub

CLEANUP: Prevent channel-t.h from being detected as C++ by GitHub

GitHub uses github/linguist to determine the programming language used for each
source file to show statistics and to power the search. In cases of unique file
extensions this is easy, but for `.h` files the situation is less clear as they
are used for C, C++, Objective C and more. In these cases linguist makes use of
heuristics to determine the language.

One of these heuristics for C++ is that the file contains a line beginning with
`try`, only preceded by whitespace indentation. This heuristic matches the long
comment at the bottom of `channel-t.h`, as one sentence includes the word `try`
after a linebreak.

Fix this misdetection by changing the comment to follow the convention that all
lines start with an asterisk.